<script>

    // 声明常量
    const PI = "3.1415926535"

    // 常量值一旦被定义，不能改变
    PI = 3 // 报错：Uncaught TypeError: Assignment to constant variable.

    // 定义常量必须初始化
    const DD // 报错：Uncaught SyntaxError: Missing initializer in const declaration

    
</script>